The purpose of this study is to explore the effects of commonly used bed and chair positions on the intensity of hemodynamic responses to the Valsalva Maneuver in normal subjects. The Valsalva Maneuver, forced expiration against a closed glottis, is a normal physiological function performed many times daily. Within seconds the force of this strain results in marked shifts of cardio- and cerebrovascular blood flow and pressure. There are clinical situations in which repeated or strenuous performance of the Valsalva is hazardous, particularly for individuals with existing cardiac or cerebro-vascular disease. Although nurses can attempt to decrease the incidences of straining, not all can be eliminated. Efforts aimed at lessening the intensity of this strain on the hemodynamic responses to the Valsalva Maneuver are imperative. We hypothesize that body position may alter the physiological responses of the Valsalva Maneuver. In Phase I of the study a minimum of 75 healthy male and 75 healthy female adults between the ages of 30-55 years of age will be tested in four commonly used bed positions (supine, lateral recumbent, thirty and seventy-degree angle upright) and a chair position. In Phase II, 30 healthy males and 30 healthy females over the age of 55 will be tested in two body positions -- those found to create the least and greatest amount of hemodynamic change in the 30-55-year-old subjects. All subjects will be asked to strain by blowing into a pressure-gauge meter to a pressure of 40 mmHg, to hold this pressure for ten seconds and to then release the strain. A strain gauge applied to the level of the diaphram will confirm the duration of the strain. Heart rate and rhythm will be recorded on a cardiac monitor and carotid artery flow velocity recorded using a transcutaneous Doppler flowmeter, prior to, during and following the Valsalva strain and until baseline measures are re-established. Baseline systolic and diastolic blood pressure will be determined, systolic blood pressure will be taken by Doppler technique at five seconds into the strain, at five seconds after the release of the strain and each minute thereafter until baseline pressure is again reached. This procedure will be repeated in all positions. Data will be analyzed by two factor analysis of variance with repeated measures, spectral density and cross-correlational techniques.